The objective of this proposal is to provide a detailed understand of the relationship between the expression of genes of the family in normal and tumor cells and patterns of drug resistance in these cells. The proposed research will be carried out using the as a model experimental system. The specific goals of the project are: 1. To complete characterization of cDNA for all members of the mdr gene family. 2. To develop analytical tools to evaluate the extent of expression of each member of the mdr gene family. 3. To determine the extent to which alternative splice patterns are used during mdr gene expression. 4. To compare the expression patterns of members of the mdr gene family in various normal tissues of the mouse. 5. To relate gene expression patterns of mdr genes in normal cells to the metabolism by these cells of drugs belonging to the mdr spectrum. 6. To identify, if possible, the endogenous substrates of the mdr system in normal cells. 7. To evaluate in detail the expression pattern of mdr genes in a series of multidrug resistant cell lines exhibit variation in drug resistance patterns and to relate mdr gene expression patterns to drug resistance patterns. 8. To perform gene transfer experiments with cloned mdr genes to more clearly define the role of each mdr gene family member in the multidrug resistance phenotype. 9. To use gene transfer techniques to test hypotheses regarding the manner in which cells of varying differentiated lineages acquire specific patterns of drug resistance. 10. To use gene transfer techniques in conjunction with site specific mutagenesis methods and/or the formation of chimeric cDNA molecules to test hypotheses regarding the location of functional sites within the mdr polypeptide.